Flat-fee affiliate tracking without third-party cookies

A merchant running a small programme finds that percentage-based apps charge more as sales grow, while flat-fee tools often rely on third-party cookies that browsers increasingly block. I build ZeroCut. The app charges a fixed monthly fee — Free, $19, or $39 — with 0% commission on tracked sales, enforced server-side. Attribution follows three signals in order: a _zc_ref cart attribute from the theme embed, a real Shopify discount code per affiliate, then the landing_site query param. A 30-day window uses first-party cookies and localStorage only; no external scripts load on the storefront. When an order is cancelled or refunded, the commission reverses automatically. Partial refunds reverse proportionally. Anything already marked paid is never rewritten. An optional hold period delays approval. The app does not store customer PII. It also does not rewrite commissions once they are marked paid, even if a later refund occurs. For very small programmes, a percentage app's free tier can cost less than any flat fee including ours.